Fluorescent ferromagnetic powder and method of making same



United States Patent 3,502,583 FLUORESCENT FERROMAGNETIC POWDER AND METHOD OF MAKING SAME Bruce C. Graham, Arlington Heights, 11]., assignor to Magnaflux Corporation, Chicago, 111., a corporation of Delaware No Drawing Filed Sept. 24, 1965, Ser. No. 490,060

Int. Cl. H01f 1/36; Gtlln 27/84, 21/16 US Cl. 252-6252 18 Claims ABSTRACT OF THE DISCLOSURE Fluorescent particles for use as flaw detection particles in a non-destructive testing procedure prepared by dispersing the particles in a reaction medium containing an aromatic aldehyde and a diamine which react to produce an azine which is precipitated directly on the surface of the ferromagnetic particles to provide a fluorescent coating.

The present invention relates to fluorescent ferromagnetic particles of the type used in non-destructive testing techniques, and to methods for their preparation.

In the original magnetic particle testing method for locating surface defects on paramagnetic bodies, the object to be examined was normally magnetized, covered with finely divided magnetic particles, and thereafter inspected after unattracted particles had been removed from the surfaces of the body under test. The remaining particles were retained in the premagnetized test piece to indicate the extent and location of surface discontinuities. This testing procedure, however, had its limitations because of difficulties arising from a lack of sensitivity, and the time consuming nature of the examination which was required.

Important improvements in the technique of testing with magnetic particles were provided by the development of particles which were combined with fluorescent materials, as described, for example, in Switzer U.S. Patent No. 2,267,999. In that patent, several methods were de scribed for combining ferromagnetic particles with fluorescent materials, including dipping the finely divided particles into a hot solution of a fluorescent material, or in a melt of the same. It was also suggested that a small proportion of a meltable transparent resin or adhesive would aid in causing the fluorescent particles to adhere to the magnetic particles. Another technique described in that patent consisted in painting the particles with fluorescent compositions by combining the two in a grinding operation until such time as the solvent present was substantially evaporated.

More recently, more sophisticated techniques have been developed for combining fluorescent materials with ferromagnetic powders. One such technique involves the precipitation of hydroxy quinoline metal complexes onto ferromagnetic particles. This procedure, however, produces fluorescent colors in the blue-green range only and provides materials which are sensitive to temperatures in excess of about 100 C.

Another technique which has been employed consists of resin bonding of pigments to ferromagnetic powders. Resin bonding requires the use of the pigment in highly expensive, highly refined form. The process and applica tion is also expensive, requiring costly equipment and large amounts of time.

One of the objects of the present invention is to provide a new method for applying fluorescent coatings to ferromagnetic particles to thereby provide an integrally coated particle suitable for use in non-destructive testing methods.

3,502,583 Patented Mar. 24, 1970 Another object of the invention is to provide an improved method for precipitating fluorescent materials in situ from a reaction medium in which the fluorescent material is formed.

Still another object of the invention is to provide a method for providing fluorescent particles having improved fluorescent intensities.

Still another object of the invention is to provide an improved fluorescent composition for non-destructive testing techniques including particles of ferromagnetic material coated with a completely adherent fluorescent coating.

A further object of the invention is to provide a fluorescent composition in which ferromagnetic particles are coated with an azine which adheres well with the underlying ferromagnetic particles.

Basically, the method of the present invention involves suspending finely divided ferromagnetic particles in a liquid vehicle which is to serve as the reaction medium for the azine formation. To this vehicle, I add both an aromatic aldehyde and a diamine capable of reacting with the aldehyde to form a fluorescent azine. The vehicle is preferably chosen so that the aldehyde and the diamine are both soluble in it before the reaction occurs, but the resulting azine is insoluble in the vehicle, so that it precipitates out of the reaction medium and onto the suspended ferromagnetic particles to provide an adherent coating of the azine on the individual particles.

The preferred class of aromatic aldehydes for use in accordance with the present invention are the orthohydroxy aromatic aldehydes such, for example, as 2-hydroxy-l-naphthaldehyde, ortho-vanillin and salicylaldehyde.

The most convenient diamine for use in connection with this process is the simplest diamine, hydrazine. However, other diamines can be used such as paraphenylenediamine and benzidine.

The overall reaction occurring in the formation of the azine is presented in the following equation:

As indicated above, the initial reaction occurs between substantially equimolar amounts of the aldehyde and the diamine, followed by a reaction of the intermediate prodnot with an additional molecular proportion of the aldehyde to form an azine. Consequently, it is advisable to use about 2 molecular proportions of thealdehyde for every molecular proportion of the diamine, although this value is not critical. The best yields seem to occur when the molecular ratio of aldehyde to diamine ranges from about 2.0 to about 0.9 to 1.

The solvent vehicle employed depends on the nature of the system, as various organic solvents can be used, as well as water in some instances. The temperature conditions are not particularly critical, as the temperatures may range from about room temperature to temperatures just below the boiling point of the solvent.

The ferromagnetic particles preferably include gamma ferric oxide, although other ferromagnetic particles such as magnetite and ordinary iron powder can be used, but not necessarily with equivalent results.

The following specific examples are for the purpose of illustrating the present invention, but it should be recognized that changes in procedure, reactants, and other variables will suggest themselves to those skilled in the art.

EXAMPLE I One hundred grams of powdered gamma ferric oxide were dispersed in 375 ml. triethanolamine and heated to C. with constant agitation. To this mixture, there was added 25 grams of 2-hydroxyl-l-naphthaldehyde until it dissolved. To this solution, there was added 475 m1. of water at 80 C. After minutes of stirring, a solution of 2.5 ml. of hydrazine in 22.5 ml. of isopropanol was added. The resulting mixture was withdrawn from heat and the stirring was increased to a maximum. After 3 minutes, 850 ml. of water were added over a minute period. The resulting particles were filtered, washed and dried. The yield of pigment was 74%, based upon the initial reactants. The product had a fluorescence of two to three times as bright as a comparable commercial material. The oxide particles were completely and uniformly coated with the pigment which had a yellow-green fluoresoence.

EXAMPLE II The same procedure was carried out as in Example I, but using 100 grams of gamma Fe O 21.7 grams of orthovanillin and 8.64 grams of paraphenylenediamine. The oxide particles were uniformly and completely coated with a pigment, which exhibited a red fluorescence.

EXAMPLE III The procedure of Example I was repeated using 100 grams of gamma Fe O 17.4 grams of salicylaldehyde, and 14.7 grams of benzidine. The coated particles recovered from this procedure exhibited a definite green fluorescence.

EXAMPLE IV The procedure of Example I was followed using 100 grams of gamma Fe O 21.7 grams of ortho-vanillin, and 14.7 grams of benzidine. The coated particles were uniformly covered with the pigment which had an orange fluorescence.

EXAMPLE V The procedure of Example I was followed except that the triethanolamine solvent was eliminated, substituting an additional amount of water in its place. One hundred grams of gamma Fe O were dispersed in the medium and coated with the reaction product obtained by reacting 17.4 grams of salicylaldehyde with 2.56 grams of hydrazine. The coated particles exhibited a green fluorescence.

EXAMPLE VI The procedure of Example V was followed, using 19.7 grams of 2,4-dihydroxybenzaldehyde along with 2.56 grams of hydrazine and 14.7 -ml. of dimethyl formamide. The aldehyde was dissolved in half the water and the amine in the other half. The particles of gamma Fe O were dispersed in this medium, and exhibited a yellowish green fluorescence.

EXAMPLE VII About 19.7 grams of 2,4-dihydroxybenzaldehyde were dissolved in 510 ml. dimethyl formamide at room temperature. About 2.04 grams of hydrazine and 1.70 grams of p-phenylenediamine were dissolved in 340 ml. of water at 80 C. The mixture was stirred for 5 minutes and was followed by the addition of 850 ml. of cold water, with stirring for an additional 5 minutes. The coated iron oxide particles were filtered, washed and dried to produce a green fluorescent product.

EXAMPLE VIII About 13.9 grams of salicylaldehyde and 5.00 grams of hydroxynaphthaldehyde were dissolved in 510 ml. dimethyl formarnide at room temperature. About 2.56 grams of hydrazine were dissolved in 340 ml. of cold water. These solutions were mixed, stirred for 5 minutes, with the addition of 850 m1. of water mixed an additional 5 minutes, and then filtered, washed and dried. The product was a bright golden yellow.

EXAMPLE IX About 13.9 grams of salicylaldehyde and 5.00 grams of hydroxynaphthaldehyde were dissolved in 510 ml. di-

methylformamide at room temperature. Approximately 2.30 grams of hydrazine and 0.86 grams of p-phenylenediamine were dissolved in 340 ml. of water at C. After mixing, stirring for 5 minutes, followed by the addition of 850 ml. of cold water, further mixing, filtering, washing and drying, the product exhibited a yellow fluorescence on the iron oxide particles.

From the foregoing, it will be understood that the process of the present invention provides a convenient and relatively rapid manner for uniformly coating ferromagnetic particles with an adherent fluorescent composition. The fluorescent material is tightly adherent to the particles, instead of being merely physically trapped among them. The recovered particles are completely suitable for use in commercial non-destructive testing procedures employing ferromagnetic particles.

I claim as my invention:

1. A fluorescent flaw detection composition consisting essentially of particles of a ferromagnetic material integrally coated with a fluorescent aromatic azine.

2. A fluorescent flaw detection composition consisting essentially of particles of gamma ferric oxide integrally coated with a fluorescent aromatic azine.

3. A fluorescent flaw detection composition consisting essentially of particles of gamma ferric oxide integrally coated with a fluorescent azine resulting from the reaction of an aromatic aldehyde with a diamine.

4. A fluorescent flaw detection composition consisting essentially of particles of gamma ferric oxide integrally coated with a fluorescent azine resulting from the reaction of an orthohydroxy aromatic aldehyde and a diamine.

5. A fluorescent flaw detection composition consisting essentially of particles of gamma ferric oxide integrally coated with a fluorescent azine resulting from the reaction of an aromatic aldehyde with hydrazine.

6. A fluorescent flaw detection composition consisting essentially of particles of gamma ferric oxide integrally coated with a fluorescent azine resulting from the reaction of hydroxy-naphthaldehyde and hydrazine.

7. A fluorescent flaw detection composition consisting essentially of particles of gamma ferric oxide integrally coated with a fluorescent azine resulting from the reaction of ortho-vanillin and paraphenylenediamine.

8. A fluorescent flaw detection composition consisting essentially of particles of gamma ferric oxide integrally coated with a fluorescent azine resulting from the reac tion of salicylaldehyde and benzidine.

9. A fluorescent flaw detection composition consisting essentially of particles of gamma ferric oxide integrally coated with a fluorescent azine resulting from the reaction of ortho-vanillin and benzidine.

10. A fluorescent flaw detection composition consisting essentially of particles of gamma ferric oxide integrally coated with a fluorescent azine resulting from the reaction of salicylaldehyde and hydrazine.

11. The method of producing fluorescent coated ferromagnetic particles 'which comprises dispersing said particles in a reaction medium in which said particles are insoluble, and reacting an aromatic aldehyde with a diamine in said reaction medium whereby the azine produced by the resulting reaction deposits on said particles as a fluorescent coating.

12. The method of producing fluorescent coated ferromagnetic particles which comprises suspending finely divided ferromagnetic particles in a liquid vehicle in which said particles are insoluble, adding to said vehicle both an aromatic aldehyde and a diamine capable of reacting with said aldehyde to form a fluorescent azine, said aldehyde and said diamine being soluble in said vehicle, but the resulting azine being insoluble in said vehicle, and reacting said aldehyde with said diamine to cause precipitation of said azine onto the suspended particles.

13. The method of claim 12 in which said aromatic aldehyde is an ortho-hydroxy aromatic aldehyde.

6 14. The method of claim 12 in which said diamine is References Cited hydrazine.

15. The method of claim 12 in which said aromatic UNITED SFJFATES PATENTS aldehyde is hydroxy-naphthaldehyde and said diamine is 2,818,432 12/1957 Klrby 2523O1-2 hydrazine 2,864,771 12/1958 Sw1tzer et a1. 25262.52 16. The method of claim 12 in which said aromatic 5 2936387 5/1960 Kazenas 252 301-3 d h glgellggleiriz'ortho vamlhn an said dlamme 1s parap eny HELEN M. MCCARTHY, Primary Examiner 17. The method of claim 12 in which said aromatic ROBERT D. EDMONDS, Assistant Examiner aldehyde is salicylaldehyde and said diamine is benzidine. 10

18. The method of claim 12 in which said aromatic U.S. Cl. X.R. aldehyde is ortho-vanillin and said diamine is benzidine. 252-3013 

